The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs.
For example, as the semiconductor fabrication continues to shrink pitches below 20 nm nodes, traditional i-ArF photoresists confronted a huge challenge. The optical restriction leads to resolution and lithography performance that cannot meet targets. Extreme ultraviolet (EUV) lithography has been utilized to support critical dimension (CD) requirements of smaller devices. EUV lithography employs scanners using radiation in the EUV region, having a wavelength of about 1 nm to about 100 nm. Some EUV scanners provide 4× reduction projection printing onto a resist film coated on a substrate, similar to some optical scanners, except that the EUV scanners use reflective rather than refractive optics. EUV lithography has imposed a complex set of requirements upon the resist film.
The photo acid generator (PAG) in ArF resist absorbs 193 nm wave and generates photoacid, and the acid will proceed 1000 times chemical amplifier reaction (CAR) and deprotect acid labile group (ALG). Different with 193 nm ArF resist, EUV will let sensitizer generate secondary electron. The secondary electron's energy is similar with 193 nm energy and is absorbed by PAG, which further generates photoacid and proceeds to CAR reaction after absorbing secondary electron, like 193 nm ArF resist. However, the EUV resist still suffers energy efficiency and other related issues due to chemical structure of known sensitizers, low source power for EUV tool, and factors. What are needed are a photoresist and a method using the photoresist to have improvements in this area.